This invention relates to an X-ray tomography apparatus and more particularly to the apparatus for obtaining a sectional image of an object e.g. a patient while moving an X-ray source and a photographic film around the center of the cross section of the patient in the mutually opposing directions in a predetermined two- or three-dimensional orbit of S-shaped, spiral, circular, elliptic motion or combinations thereof.
In this type of the device an iris diaphragm is fixedly attached to the front side of the X-ray source, travelling together in an orbit to regulate the field of X-radiation into a given cross section. With the iris diaphragm so constructed, however, the X-radiation area onto the patient varies with the orbital position of the source, resulting in the failure to obtain a good X-ray image.